Bài tập 1 trang 124 VBT Toán 5 tập 2

b)

\(\displaystyle{5 \over 9} \times {{12} \over {25}} =\dfrac{5\times 12}{9\times 25 } =\dfrac{5\times4 \times 3 }{3\times 3 \times 5 \times 5} =\dfrac{4}{15}\)

\(\displaystyle{{12} \over {11}}:{{36} \over {55}} = \dfrac{12}{11}\times \dfrac{55}{36} =\dfrac{12\times 55}{11\times 36} =\dfrac{12\times 11 \times 5}{11\times 12 \times 3} =\dfrac{5}{3 }\)

\(\displaystyle{9 \over {55}} \times 22= \dfrac{9\times 22}{55}= \dfrac{9\times 11 \times 2}{11 \times 5}=\dfrac{18}{5}\)

\(\displaystyle{{144} \over 7}:36=\dfrac{144}{7}\times \dfrac{1}{36}=\dfrac{144\times 1}{7 \times 36}=\dfrac{36\times 4\times 1}{7 \times 36}=\dfrac{4}{7}\)

-- Mod Toán lớp 5 HỌC247